### ASA 127th Meeting M.I.T. 1994 June 6-10

## 3aUW16. An efficient and robust method for underwater acoustic normal mode
computations.

**Scott J. Levinson
**

**
Robert A. Koch
**

**
Evan K. Westwood
**

**
Stephen K. Mitchell
**

**
Carol V. Sheppard
**

**
**
*Appl. Res. Lab., Univ. of Texas at Austin, Austin, TX 78713
*

*
*
An efficient, numerically robust algorithm for calculating acoustic
depth-dependent normal modes for stratified fluid, multichannel ocean
environments is described. An Airy-layered solution is used, and eigenvalues
are found by a process which avoids the numerical instabilities associated with
evanescent (nonoscillatory) depth dependence. Eigenfunction solutions are valid
for multichannel environments. Computation time increases only linearly with
frequency or number of modes. This algorithm (called ModeLab), is compared with
KRAKEN [M. B. Porter and E. L. Reiss, J. Acoust. Soc. Am. 77, 1760--1767
(1985)] and with a model designed for fast cw calculations [K. J. McCann and F.
Lee-McCann, J. Acoust. Soc. Am. 89, 2670--2676 (1991)]. ModeLab achieves the
fastest computational speeds by more than an order of magnitude, and
simultaneously provides eigenvalue accuracies comparable to the best available
from KRAKEN. [Work supported by the Advanced Surveillance and Prediction System
(ASAPS) Program of the Space and Naval Warfare Systems Command (SPAWAR, PMW
183-32).]